Drop __mul_used from IrOp::Mul codegen and __div_used from IrOp::Div
/ IrOp::Mod codegen (modulo reuses the same routine). The linker
skips gen_multiply / gen_divide for programs that never emit the
markers, following the same pattern already used by __audio_used /
__ppu_update_used / __sprite_cycle_used.
The optimizer already rewrites multiplies and divides by constant
powers of two into shifts (and modulo by constant powers of two
into masks), so the markers only fire for genuinely runtime math.
A program like `examples/comparisons.ne` that never multiplies or
divides now reclaims ~56 bytes of PRG; programs that use only one
of the two reclaim the other's share.
Audio goldens flip for every example that uses audio. The .ne
sources are unchanged and the pixel goldens are byte-identical —
the audio stream differs only because removing the math routines
shifts the audio tick's absolute address in PRG by 56 bytes, which
changes which of its internal branches cross 6502 page boundaries
and therefore the per-frame cycle count of a single NMI by 1-5
clocks. Over 180 frames the accumulated drift shifts APU register
write timing enough to render a different digital sample stream
at the same logical wave shape. Expected consequence of ROM-layout
change under cycle-accurate emulation; documented path per
CLAUDE.md "Updating goldens".
https://claude.ai/code/session_016kM6P7PukktBDqTZexrrAN
The IR codegen lowers `i -= 1` (and friends) into a `LoadImm temp,
1; Sub d, i, temp; StoreVar i, d` triple, and the optimizer
strength-reduces the Sub+StoreVar pair into `DEC i`. The
constant-load-into-A that used to feed the Sub stays around as a
dead `LDA #1`:
LDA #1
DEC ZeroPage(rem)
JMP Label("__ir_blk_while_cond_…")
`remove_dead_loads` was set up to drop exactly this pattern but
gave up at the trailing `JMP` because it couldn't reason about
flow. Extend it to follow one unconditional `JMP <label>` to its
target and resume the dead-store scan from the next instruction.
The first instruction past the loop-condition label is reliably an
`LDA loop_var`, which overwrites A without reading it — so the
`LDA #1` is correctly identified as dead.
Conditional branches still end the scan (their not-taken path is
unconstrained) and only one JMP is followed (to keep the analysis
local). For SHA-256 specifically this drops two `LDA #1`s per
iteration of the rotate/shift bit-loops — about 1K cycles per
block. The same pattern fires across most examples' loop tails.
Verified: cargo test/clippy/fmt clean on rustc 1.95.0; emulator
harness 34/34; reproducibility diff clean; SHA-256 of "NES" still
computes to AE9145DB…4E0D. The cycle drift refreshes the four
audio hashes / golden frames timing-sensitive examples already
tracked.
https://claude.ai/code/session_01FRmSBruVWCufm3LsUVMs8v
Every NEScript condition (`if x < N`, `while i < end`, etc.)
lowers in two IR ops: `CmpX(d, a, b)` materializes a 0/1
boolean into temp `d`, and the block's terminator
`Branch(d, t, f)` reads `d` and branches on it. The codegen
faithfully emitted both halves — `LDA / CMP / branch-to-true /
LDA #0 / JMP done / true: LDA #1 / done:`, then later
`LDA d_slot / BNE branch_t / JMP branch_f` — about 14 cycles +
13 bytes per condition.
The 6502's natural pattern is one `CMP` + one branch on the
flags it just set: 8 cycles, no register-clobber, no temp slot.
Detect the canonical pattern in `gen_block` (last op is an 8-bit
`CmpX` whose dest temp is what the terminator branches on, with
no other uses) and emit the fused form directly via a new
`gen_cmp_branch` helper. The temp's allocation, store, load, and
the terminator's branch fall away.
Bookkeeping subtlety: the source temps `a`/`b` must be retired
*after* the fused emit, not before — the original `gen_op` order
is "emit body of op, then `retire_op_sources`". Decrementing
their use counts before the CMP would free their slots while
they were still live; `load_temp(a)` would then re-allocate `a`
to whatever stale slot the free list popped next. Got hit by
this on the first attempt — the SHA-256 example dutifully
returned all-zero hashes until the order was fixed.
Updated `ir_codegen_local_label_suffix_is_bank_namespaced`: the
test was relying on `if x == 0` to emit `__ir_cmp_*` labels for
its bank-namespacing check, which the fusion now collapses into
direct branches. Switched the test source to a shift-by-variable
pattern (`x = x << n`), which always emits `__ir_shift_loop_*`
labels regardless of future cmp/branch optimizations.
Cycle savings: ~6 cycles per condition. The SHA-256 rotate
loops alone account for ~9K cycles per block. Across all
examples the cycle drift shows up as audio-tick phase shifts
in five timing-sensitive ROMs (`audio_demo`, `friendly_assets`,
`noise_triangle_sfx`, `platformer`, `sfx_pitch_envelope`); the
goldens for those are refreshed in this commit, plus
`platformer.gif` (the only demo gif whose bytes actually moved).
Verified: cargo test/clippy/fmt clean on rustc 1.95.0;
emulator harness 34/34; reproducibility diff clean; SHA-256 of
"NES" still computes to AE9145DB…4E0D.
https://claude.ai/code/session_01FRmSBruVWCufm3LsUVMs8v
`const_fold_block`'s per-block dead-code pass was collecting temp
usage from only the block it was folding, so a `LoadImm` whose
destination is consumed by a *sibling* block (for example via the
merge block's branch terminator) was incorrectly treated as dead
and dropped. The `and` / `or` short-circuit lowering emits exactly
that shape: the false path writes `LoadImm(result, 0)` and joins
with the right path at an `and_end` / `or_end` block whose branch
terminator reads `result`. After the DCE the false path's store
was gone, leaving the zero-page result slot to carry whatever value
the *previous* `and` / `or` evaluation had written there — stale
data that bled into subsequent conditional branches.
I found this while instrumenting `examples/platformer.ne` through a
puppeteer-driven jsnes harness, stepping one frame at a time and
snapshotting the full zero-page trace of each scenario (title-skip,
hold-right, hold-left, jump-spam, coin-drift, enemy-stomp, long-run).
In a clean idle run the enemy-1 stomp bounce (`rise_count = 6`,
`fall_vy = 0`) fired at emulator frames 83 and 96 with `camera_x`
= 61 and 74, i.e. with `e1_sx` = 39 and 26, nowhere near the
intended `[72, 96)` pickup window. The trigger turned out to be
the slot alias: every time `c2_sx` landed in its pickup window
(so the coin-2 `and` stored 1 into ZP(130)) and the player was
mid-fall at or past `player_y = 152`, the enemy-1 stomp `and`
short-circuited to its false path, left ZP(130) at 1, and the
stomp `if` fired on stale data.
The fix is to compute function-wide source-operand usage once before
folding each function's blocks and OR it into the per-block liveness
check, so a LoadImm is only dropped if nobody — neither its own
block nor any other block in the function — reads the temp. Added a
regression test (`const_fold_preserves_loadimm_used_by_sibling_branch`)
that builds the exact CFG shape the `and` lowering emits and
verifies the false-path `LoadImm(result, 0)` survives optimization.
Impact on the example ROMs:
- `examples/platformer.nes`: enemy-1 stomp now fires only when
`e1_sx ∈ [72, 96)`, as the source intends. The pixel golden is
unchanged (`player_y` converges back to the ground line before
frame 180), but the audio hash flips because the spurious
`play hit` sfx calls during coin-2 passage are gone. Committing
the new `tests/emulator/goldens/platformer.audio.hash`.
- `examples/logic_ops.nes`, `examples/bitwise_ops.nes`,
`examples/match_demo.nes`, `examples/mmc3_per_state_split.nes`,
`examples/two_player.nes`: byte-different but observably
unchanged — their pixel + audio goldens still match to the byte.
They exercise `and` / `or` in the source and now compile through
the corrected DCE.
All other example ROMs are byte-identical to pre-fix. `cargo fmt`,
`cargo clippy --all-targets`, `cargo test --release` (498 tests),
and `tests/emulator/run_examples.mjs` (22/22 goldens) are clean.
https://claude.ai/code/session_013Bi4H4YQ5or5HtMB4doUFi
The compiler is deterministic: rebuilding any example produces
a byte-identical ROM, verified across all 22 examples and all
four mappers (NROM, MMC1, UxROM, MMC3). That means the .nes
files are reproducible artefacts and can live next to their
sources without drift.
Benefits:
- Users can clone the repo and open any example in an emulator
without installing a Rust toolchain or running the compiler.
- The emulator harness can trust examples/*.nes directly, so its
CI job no longer needs a compiler build or a "compile all
examples" loop — it just boots jsnes against the committed
ROMs and diffs each against its golden.
- ROM diffs in PRs are now meaningful: "this compiler change
flipped 17 bytes in hello_sprite.nes" is visible review
signal, not hidden behind the emulator golden.
Guard rails so the ROMs don't drift from their sources:
- .gitignore no longer excludes *.nes.
- The `examples` CI job rebuilds every .ne into /tmp and fails
loudly (with a GitHub error annotation pointing at the exact
cargo command to rerun) if any committed ROM differs.
- scripts/pre-commit does the same check locally.
- CLAUDE.md now states that editing a .ne file requires
rebuilding its .nes in the same commit, so future agents
won't miss the invariant.
Total footprint: 22 ROMs, 624 KB (avg 28 KB each — most are
NROM 24 KB; two banked examples are larger).
https://claude.ai/code/session_01BcCcHi6FUmTh8jC7UgkA3A
